Iron as a component of haemoglobin and the cell haemins is one of the most important biocatalysts in the human organism. Disorders of iron metabolism and in particular iron deficiency and perturbations of iron distribution and utilization in chronic general illnesses are among the most frequently overlooked or misinterpreted diseases. One of the main reasons for this is that the determination of transport iron in the serum or plasma which is used in conventional diagnostics does not allow a representative estimation of the total body iron stores due to short-term variations.
The ability to precisely determine the iron storage protein ferritin in plasma provided a method for determining the total body iron stores and thus allowed a more rapid and reliable diagnosis especially of iron deficiency states. Ferritin is an indicator of the amount of storage iron. The soluble transferrin receptor (sTfR) indicates the iron requirements of the cell and erythropoiesis activity. The sTfR/log ferritin index is a measure of the depletion of the iron stores and of the functional iron compartments. In chronic inflammatory diseases such as in infections and especially tumour diseases, iron is redistributed with a relative overload of the iron stores accompanied by a relative deficiency of iron supply to the erythropoietic cells.
Due to the very limited capacity to absorb iron, the iron requirements can only be met by recycling functional iron. It is stored in the form of ferritin and haemosiderin. Each cell is able to take up a surfeit of iron by synthesizing ferritin and the basic mechanisms for this are identical in all types of cells. The transferrin-iron3+ complex is bound to the transferrin receptor of the cell membrane. The uptake of iron can be regulated by the transferrin receptor expression. In addition iron induces the synthesis of apoferritin. Hence in the majority of metabolic situations a representative proportion of the synthesized ferritin is released into the blood plasma.
However, even if the above-mentioned parameters are employed, it is not in practice possible or very difficult to routinely determine and differentiate between various iron states.
Therefore an object of the present invention was to provide a method which enables the reliable detection of disorders of iron metabolism in a simple manner.